Field of the Invention
This invention concerns welding apparatus and methods and more particularly for the so-called TIG and MIG type welding, i.e., tungsten inert gas and metal inert gas welding. In these methods, an electrode has an electrical potential applied between it and the workpiece to cause an arc to be formed between the electrode and the workpiece. The heat generated by the arc causes melting of the base metal in order to form the weld.
In order to prevent the migration of atmospheric nitrogen and oxygen into the weld and resultant poor weld quality as well as contamination of the electrode itself, an outer shielding flow of an inert gas is employed which greatly reduces the presence of oxygen and nitrogen in the weld area. Argon gas is commonly employed, applied through an annular clearance space surrounding the electrode to provide a more or less complete envelopment of the electrode and weld area for this purpose.
The gases most commonly used are argon and helium, since nitrogen, while being inert, tends to adversely affect the quality of the weld. These gases are relatively costly and in accordance with the rate of flow of these gases required for adequate shielding, the cost of the process correspondingly is affected.
In order to reduce the flow of shielding gas for adequate weld quality, a method is sometimes used in which a flow of a cheaper gas such as carbon dioxide or air located radially outward from the space through which the argon flows. While relatively effective in precluding the dissipation of the argon or helium flow, the higher rates of gas flow used for effective shielding tend to cool the metal to produce an enhanced quenching effect of the weld, adversely affecting the quality of the weld metal grain structure. The weld is adversely affected either by too rapid heating or cooling of the weld metal, this effect causing undesirable changes in the crystal or grain size and residual stresses in the surrounding metal.
In order to be conveniently usable in production, control over the flow of shielding gas should be integrated with the welding controls, such as to be suitable for automation of the equipment and/or rapid manipulation by workers utilizing manual setups.
It has heretofor been recognized that the addition of hydrogen gas mixed into the shielding gas, burns, consuming oxygen to reduce the oxide formation on the weld and improving the shielding effect on the argon.
However, there is a tendency for the presence of the hydrogen gas to create porosity and pin holes in the weld metal, probably due to formation of water vapor upon burning.
There has also been heretofor employed hydrogen gas jetted into the vicinity of the argon flow. Neither approach produces complete shielding of the inert gas primary shielding flow.
The hydrogen gas intermixed in the argon gas did burn, which tended to reduce the oxides but so intermixed did not provide an effective confinement of the argon gas flow, although the volume of the burning hydrogen increased the size of the envelope of shielding gas and thereby to some extent reduced the flow of argon gas required for adequate shielding.
Such separate hydrogen gas jetting that has heretofor been employed has been relatively crude and not integrated into the machine controls such as to provide convenient usage thereof.
Accordingly, it is an object of the present invention to provide a more effective shielding of an arc welding torch of the type employing inert gas as a primary shielding flow surrounding the welding electrode and weld area.
It is still another object of the present invention to provide an improved inert gas shielding arrangement in which reduced inert gas flow is enabled while producing welds of superior quality.
It is still another object of the present invention to provide a hydrogen gas flow at the weld torch without producing porosity in the resultant weld.
It is yet another object of the present invention to provide such hydrogen inert gas shielding arrangement in which the shielding gas flow control is entirely integrated into the welding controls.
It is a still further object of the present invention to provide such hydrogen inert gas shielding for an arc welding torch in which the hydrogen gas provides a completely surrounding envelope about the exterior of the inert gas flow path.